JP2008309776A - Optical fiber vibration sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber vibration sensor with high detection sensitivity. <P>SOLUTION: This optical fiber vibration sensor includes a light source, an optical receiver, an optical dividing/coupling part, a signal processing unit, and a fiber loop part made of an optical fiber. Part of the optical fiber composing the fiber loop part is installed within a housing of a main body of the optical fiber vibration sensor and another part of the optical fiber composing the fiber loop part is installed outside the housing as a vibration detecting optical fiber. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical fiber vibration sensor with good detection sensitivity.

  Conventionally, a physical disturbance (vibration) applied to an optical fiber by propagating light in both directions on the left and right in a loop-shaped optical fiber, interfering with the circular light in both directions, and measuring the intensity change of the interference light. As a sensor for detecting the impact), a Sagnac interference type vibration sensor as shown in FIG. 7 is known.

  In FIG. 7, an optical fiber vibration sensor 101 includes a light source 102, a light receiver 103, a fiber loop portion 104 made of an optical fiber, and makes the light from the light source 102 enter the fiber loop portion 104 in both directions. The optical branching / coupling unit 105 that guides the interference light to the light receiver by interfering with the left and right outgoing light emitted from the fiber loop unit 104 and the reception signal of the interference light received by the light receiver 103 are processed. A signal processing unit 106 is provided, and an optical fiber constituting the fiber loop unit 104 is laid on a vibration detection object as a vibration detection optical fiber.

  When the fiber loop portion 104 is laid on the fence, when the fence is shaken, a light reception signal similar to that when a rotational angular velocity is generated in the fiber loop portion 104 is obtained. The Sagnac interferometer vibration sensor cannot detect the absolute value of the frequency or amplitude, but it examines the change in the received light signal when a specific object hits the fence in advance and sets it as a comparative sample. The change in signal can be compared with a comparative sample to recognize that a particular hit the fence. This method can be applied to detect that a person has shaken a fence in a restricted area, a private house, etc., or to detect that a protective wall of a road or a railway has been shaken by falling rocks.

Japanese Patent Laid-Open No. 2003-247887

  However, the Sagnac interference vibration sensor disclosed in Japanese Patent Application Laid-Open No. 2003-247887 has a sensitivity characteristic that the sensitivity varies depending on the location of the fiber loop portion 104. This is because, in the vicinity of the center portion in the loop length direction of the fiber loop portion 104, light on both the left and right sides branched by the light branching and coupling portion passes at approximately the same time, and therefore, a phase difference due to vibration is unlikely to occur. In particular, the sensitivity is zero at the midpoint of the fiber loop portion 104. For this reason, in the vibration detection target object in which the fiber loop portion 104 is laid, the sensitivity for detecting vibrations varies depending on the location.

  Therefore, an object of the present invention is to provide an optical fiber vibration sensor that solves the above problems and has good and uniform detection sensitivity.

  To achieve the above object, the present invention provides a light source, a light receiver, a light branching / coupling unit for branching or coupling light, a signal processing unit for processing a received signal from the light receiver, and the light branching / coupling unit. And a part of the fiber loop part that propagates the light branched off as left-handed light and right-handed light, and the light source, the light receiver, the light branching and coupling part, the signal processing unit, and the fiber loop part. An optical fiber vibration sensor in which one side of the optical branching and coupling unit is connected to the light source and the light receiver and the other side is connected to the fiber loop unit, the optical branching and coupling unit includes the light source and A first optical coupler to which the light receiver is connected; a polarizer that linearly polarizes light from the first optical coupler; and the light from the polarizer is branched and incident on the fiber loop portion. A second optical coupler that couples the light emitted from the fiber loop unit, and a phase modulator is provided in the fiber loop unit, and a part of the optical fiber constituting the fiber loop unit is an optical fiber delay unit The remaining optical fibers constituting the fiber loop portion are laid outside the casing as vibration detection optical fibers.

  The optical fiber delay unit may have a length at least half that of the optical fiber constituting the fiber loop unit.

  The vibration detection optical fiber may be formed by connecting one end of two optical fibers arranged in parallel directly or using a folding optical fiber.

  The vibration detection optical fiber may be provided in a flexible tube while the fiber loop portion provided outside the casing is folded back.

  You may provide the said housing | casing and the said optical fiber for vibration detection provided so that attachment or detachment with respect to this housing | casing was possible.

  The optical fiber used for the light source, the light receiver, the optical branching and coupling unit, and the optical fiber constituting the fiber loop unit may be a polarization-maintaining fiber.

The present invention further includes a light source;
A receiver,
A fiber loop with a loop structure that propagates counterclockwise and clockwise light;
One side is connected to the light source and the light receiver, and the other side is connected to the fiber loop unit. An optical branching and coupling unit that inputs to the receiver,
It consists of a phase modulator that gives a phase difference between left-handed light and right-handed light,
An optical fiber vibration sensor is provided in which a part of the fiber loop portion constitutes a sensor cable laid on a measurement object, and at least half of the fiber loop portion is provided outside the sensor cable.

  The sensor cable may be composed of two optical fiber portions arranged in parallel.

  A part of the half of the fiber loop portion may constitute an optical fiber delay portion.

  The light branching and coupling part may have a polarizer.

  The two optical fiber portions may be formed by folding back one optical fiber.

  The present invention exhibits the following excellent effects.

  (1) Good detection sensitivity.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

(Configuration of optical fiber vibration sensor 1)
As shown in FIGS. 1, 2 (a), 2 (b), 3 (a), 3 (b), and 4, the optical fiber vibration sensor 1 according to the present invention includes a housing 10 a. The vibration sensor main body 10 including the vibration sensor main body 10 and the vibration detection optical fiber 9 laid outside the housing 10a of the vibration sensor main body 10 are configured.

  As shown in FIG. 1, the vibration sensor main body 10 includes a light source 2, a light receiver 3, an optical branching / coupling unit 5 that branches or combines light, and a signal processing unit 7 that processes a received signal from the light receiver 3. And a housing 10a, and a fiber loop portion (optical closed circuit) 4 partially laid outside the housing 10a as the vibration detecting optical fiber 9.

  The fiber loop unit 4 includes a phase modulator 6 and an optical fiber delay unit 8 in a housing 10a. The optical fiber delay unit 8 includes an optical fiber 8 b having a half length of the fiber loop unit 4. The detailed configuration of each part will be described later.

  A laser diode (LD) or a super luminescent diode (SLD) with a short coherence distance is used as the light source 2, and a photodiode (PD) is used as the light receiver 3. Each of the light source 2 and the light receiver 3 is connected to an optical fiber for connection, and is connected to an optical branching and coupling unit 5 described later.

  The optical branching and coupling unit 5 includes a first optical coupler 18a connected to the light source 2 and the light receiver 3, a second optical coupler 18b connected to a fiber loop unit to be described later, a first optical coupler 18a, and a second optical coupler. And a polarizer 19 connected to 18b.

  As shown in FIGS. 1 and 2 (a), the polarizer 19 is formed by forming a part of an optical fiber 19a connecting the first optical coupler 18a and the second optical coupler 18b in a coil shape, This is a fiber-type polarizer with increased birefringence.

  As shown by the dotted line in FIG. 1, the fiber loop unit 4 is connected to the second optical coupler 18b constituting the optical branching and coupling unit 5, and the light branched by the second optical coupler 18b is counterclockwise. -It consists of an optical fiber in which an optical path is formed so as to circulate (propagate) clockwise.

  Since the interference light intensity of the counterclockwise light and the clockwise light that circulates around the fiber loop portion 4 is proportional to cos φ (φ; Sagnac phase difference), the detection sensitivity for a subtle phase difference is lowered. Therefore, in order to increase the detection sensitivity for a subtle phase difference, a phase modulator 6 is provided that generates a phase difference equivalent to π / 2 in the counterclockwise light and the clockwise light.

  The phase modulator 6 provided in the fiber loop unit 4 applies phase modulation with a relative time delay to the counterclockwise light and clockwise light propagating through the fiber loop unit 4.

  In this embodiment, as shown in FIG. 2B, the phase modulator 6 is formed by winding an optical fiber 6b that forms a part of the fiber loop portion 4 around a cylindrical piezoceramic (PZT) 6a. The optical fiber 6b wound around the cylindrical PZT 6a is expanded and contracted by a voltage applied to the cylindrical PZT 6a to modulate the phase of the propagation light.

  The signal processing unit 7 processes the reception signal output from the light receiver 3 to identify the location where the vibration has occurred, the magnitude of the vibration, and the like. In addition, the output level of the light source 2 is controlled, and the modulation level of the phase modulator 6 is also controlled.

  As shown in FIGS. 3A and 3B, the optical fiber delay unit 8 is wound around the bobbin 8a and the bobbin 8a so that the optical fiber 8b having a predetermined length is concentrated in one place. Is. In the present embodiment, the optical fiber 8 b of the optical fiber delay unit 8 has a length corresponding to half or more of the optical path length of the fiber loop unit 4. The optical fiber 8b of the optical fiber delay unit 8 is formed by a part 8b-1 wound in one direction (CW) and a part 8b-2 wound in the opposite direction (CCW), and a part wound in one direction (CW part) ) In the portion (CCW portion) 8b-2 wound in the opposite direction to 8b-1, the fiber length and the number of turns are made equal to each other, and the cross-sectional areas of the CW portion 8b-1 and the CCW portion 8b-2 of the optical fiber 8b (Loop area) is formed to be equal. For example, the intermediate point M1 of the optical fiber 8b of the fiber loop portion 4 constituting the optical fiber delay unit 8 is appropriately determined, and the one side portion and the opposite side portion folded at the intermediate point M1 are aligned in parallel and the periphery of the bobbin 8a. It is good to form by winding up.

  Thereby, even when an impact or vibration is applied to the vibration sensor main body 10 (that is, the housing 10a) or the vibration sensor main body 10 rotates, the optical fiber delay unit 8 accommodated in the housing 10a performs a rotational motion. No detection occurs, and no malfunction occurs in vibration detection.

  On the other hand, the vibration detection optical fiber 9 is laid on a vibration detection object and is preferably formed in the form of FIG.

  The optical fiber vibration sensor 1 of FIG. 1 differs from the conventional apparatus in the following points. In the conventional apparatus, the entire length of the fiber loop portion 104 is laid on the vibration detection object. On the other hand, in the optical fiber vibration sensor 1 shown in FIG. 1, the fiber loop unit 4 includes an optical fiber 8 b of the optical fiber delay unit 8 that is not laid on the vibration detection target and a vibration detection optical fiber that is laid on the vibration detection target. 9 is different.

  The optical fiber used for the light source 2, the light receiver 3, and the optical branching and coupling unit 5 and the optical fiber constituting the fiber loop unit 4 are preferably polarization-maintaining fibers.

  As shown in FIGS. 1 and 4, the vibration detecting optical fiber 9 is laid outside the housing 10 a of the vibration sensor main body 10. In the present embodiment, the vibration detecting optical fiber 9 is detachably provided to the vibration sensor main body 10. That is, the fiber loop unit 4 includes an optical fiber constituting the phase modulator 6 and the optical fiber delay unit 8 provided in the vibration sensor main body 10, and a vibration detection optical fiber 9 provided outside the vibration sensor main body 10. The optical fiber constituting a part of the fiber loop part 4 in the vibration sensor body 10 and the vibration detecting optical fiber 9 constituting the other part of the fiber loop part 4 outside the vibration sensor body 10 are a vibration sensor. They are connected by receptacles 11 and 12 provided outside the casing of the main body 10.

  As shown in FIG. 4, the vibration sensor main body 10 is provided with receptacles 11 and 12 on the outer surface of the housing 10 a and is connected to optical connectors 13 a and 13 b provided at both ends of the vibration detection optical fiber 9. Is done. As a result, the optical fiber in the vibration sensor main body 10 constituting a part of the fiber loop portion 4 and the vibration detecting optical fiber 9 constituting the other portion of the fiber loop portion 4 are connected to each other. Is configured. By providing the vibration detecting optical fiber 9 detachably with respect to the vibration sensor main body 10, the vibration detecting optical fiber 9 can be easily laid on a fence or the like.

  The vibration detecting optical fiber 9 includes two optical fibers 14a and 14b arranged in parallel, and a connecting portion 15 that connects the two optical fibers 14a and 14b at one end of the two optical fibers 14a and 14b. It is to be prepared. The two optical fibers 14 a and 14 b are accommodated in the flexible tube 16.

  Here, the entirety of the vibration detecting optical fiber 9 and the flexible tube 16 is referred to as a sensor cable 17. The sensor cable 17 includes a part of the fiber loop portion 4 and includes optical fibers 14a and 14b arranged in parallel for reciprocating light, and a flexible tube 16 that combines the optical fibers 14a and 14b. The vibration sensor main body 10 is configured to be detachable. The vibration can be detected by laying the sensor cable 17 on the vibration detection object and attaching the sensor cable 17 to the vibration sensor main body 10. For example, when the vibration detection optical fiber 9 is laid on a wire fence, the sensor cable 17 is fastened to the wire mesh using a resin fastener.

  In the present embodiment, the vibration detecting optical fiber 9 is configured using an optical fiber cable including two optical fibers 14 a and 14 b in the flexible tube 16. The connecting portion 15 removes the optical fiber coating at the tip of the optical fiber cable by a predetermined distance (for example, 10 mm) to expose the two optical fibers, and connects the two optical fibers 14a and 14b. It is formed by recoating the connecting part. Thereafter, the partially removed optical fibers 14a and 14b including the connecting portion 15 are accommodated in an optical fiber accommodation case (not shown) within a range of an allowable bending diameter.

  The storage case is made of resin or metal, and the connecting portion 15 and the removed two optical fibers 14a and 14b are fixed to the storage case by potting with resin. The vibration detecting optical fiber 9 may be configured by folding one optical fiber. However, in consideration of handling during the work of fixing the cable to the fence, an optical fiber cable having two optical fibers is used. Thus, a configuration in which two optical fibers are connected to provide the vibration detecting optical fiber 9 is more preferable.

(Operation of optical fiber vibration sensor 1)
Next, the operation of the optical fiber vibration sensor 1 will be described.

  The optical fiber vibration sensor 1 is a Sagnac interference type vibration sensor. When vibration is applied to the optical fiber 14 (that is, 14a or 14b) constituting the fiber loop portion 4, the intensity of the optical signal detected by the light receiver 3 changes. To do.

  At this time, the vibration frequency of the vibration applied to the optical fiber 14 is fm, the propagation delay time difference of the left and right light at the place where the vibration is applied (longitudinal position on the optical fiber 14) is τ, and the phase difference of the left and right light is φ Then, the phase difference φ as a function of time t is given by the following relational expression (1).

φ (t) = A · sin (2π · fm · τ / 2) · cos (2π · fm · t)
... (1)
Here, A is a constant related to the intensity (amplitude) of vibration.

  At the midpoint M1 of the fiber loop unit 4, the left-right light reaches the same time, so that the propagation delay time difference τ = 0. At this time, even if there is vibration applied to the optical fiber 14, the phase difference φ = 0 from the relational expression (1). That is, the sensitivity to vibration is zero at the midpoint M1 of the fiber loop portion 4.

  Since the propagation delay time difference τ has a specific value other than 0 at a location outside the midpoint M1 of the fiber loop portion 4, if there is vibration applied to the optical fiber 14, a value is generated in the phase difference φ. Since the propagation delay time difference τ increases as the distance from the intermediate point M1 increases, the phase difference φ is large for vibrations having the same intensity. That is, the sensitivity to vibration increases as the distance from the intermediate point M1 increases. Note that the propagation delay time difference τ is a very small value. Therefore, the sine function in the relational expression (1) can be approximated by a linear expression.

Specifically, when the total length of the fiber loop portion 4 is 400 m and the maximum value of the propagation delay time difference τ is determined from the refractive index n of the optical fiber core and the light velocity c,
τ = L · n / c
= (400 × 1.47 / (3 × 10 ⁸ ))
= 1.96 × 10 ⁻⁶
It becomes.

At this time, assuming that the vibration frequency fm is 100 Hz at the maximum, (fm · τ) is about 2 × 10 ⁻⁴ and is very small. Therefore, the sine function of the relational expression (1) can be approximated by a linear expression. Therefore, the phase difference φ is proportional to the propagation delay time difference τ. That is, the sensitivity of the Sagnac interference vibration sensor is proportional to the propagation delay time difference τ.

  Thus, the Sagnac interference type vibration sensor has a sensitivity characteristic that the sensitivity varies depending on the location of the fiber loop portion.

  FIG. 5 is a sensitivity characteristic diagram with the propagation delay time difference τ on the horizontal axis and the vibration detection signal intensity based on the phase difference φ on the vertical axis. As shown in FIG. 5, the vibration detection signal intensity is proportional to the propagation delay time difference τ. Since the propagation delay time difference τ is a function of the distance from the intermediate point M1 of the fiber loop part 4, the horizontal axis indicates the location on the fiber loop part 4, and the sensitivity characteristic diagram of the fiber loop part 4 can be obtained.

  Therefore, according to the conventional optical fiber vibration sensor 101, when the entire fiber loop portion 104 is laid on the vibration detection object, the sensitivity of detecting vibration depending on the location of the fiber loop portion 104 laid on the vibration detection object is low. It becomes uniform. Specifically, the sensitivity is zero at an intermediate point of the fiber loop unit 104. In the vicinity of the intermediate point, the sensitivity is very small. As the distance from the intermediate point increases, the sensitivity increases, and the sensitivity is maximized on the incident / exit side of the fiber loop portion 104 (in the vicinity of the optical fiber coupler).

  In the optical fiber vibration sensor 1 of the present invention, the optical fiber delay unit 8 has a length that is more than half of the total length of the optical fiber constituting the fiber loop unit 4, for example, vibrates an intermediate point M 1 of the fiber loop unit 4. It can be set as the structure provided in the receptacle part 11 which is a connection point of the one end side of the optical fiber 9 for detection, and the housing | casing 10a. Then, by connecting the other end side of the vibration detection optical fiber 9 to the receptacle part 12, the vibration detection optical fiber 9 is distanced from one end side of the vibration detection optical fiber 9 from one end side to the other end side. The sensitivity increases proportionally from zero. Further, in the connection portion 15 including the middle (folding point) C of the vibration detection optical fiber 9, the sensitivity is intermediate between the sensitivity near the receptacle portion 11 and the sensitivity near the receptacle portion 12.

  In the present invention, a sensor cable 17 is configured by providing the vibration detecting optical fiber 9 provided outside the housing 10a in one flexible tube 16, so that the sensor cable 17 is for reciprocating light. When the sensitivity distributions of the two optical fibers 14a and 14b provided in parallel with each other are overlapped, they are uniform regardless of the location in the longitudinal direction.

  FIG. 6A is a sensitivity characteristic diagram in which the horizontal axis represents the distance from the connection point of the sensor cable 17 to the vibration sensor main body 10 to the turning point C, and the vertical axis represents the vibration detection signal intensity based on the phase difference φ. is there. The sensitivity of the sensor cable 17 of the present invention is constant in the longitudinal direction as shown by the solid line in FIG. As shown by the broken line, it can be seen that the sensitivity of the two optical fibers 14a and 14b is superimposed and becomes a constant value.

  Table 1 shows the clockwise and counterclockwise distances at the measurement points P1 to P6 of the fiber loop portion 4 shown in FIG. 4 with the total length of the fiber loop portion being 4L. At this time, the optical fibers other than the optical fiber delay unit 8 and the vibration detection optical fiber 9 are short enough to be ignored compared to the optical fiber 8b and the vibration detection optical fiber 9 of the optical fiber delay unit 8. To do. For example, the total length of the fiber loop portion is 400 m, and the optical fiber constituting the phase modulator 6 is 1 m.

  In FIG. 4, x is a distance between the sensor body 10 and the measurement point of the sensor cable 17. As shown in Table 1, the clockwise distance and the counterclockwise distance are (2L, 2L) at the measurement point P1 connected to the receptacle 11. At the measurement point P6 connected to the optical receptacle 12, the clockwise distance and the counterclockwise distance are (4L, 0). Here, the length of the optical fiber 8b of the optical fiber delay unit 8 is 2L, and the length of the vibration detecting optical fiber 9 is 2L. At measurement points P2 and P5 at a distance x from the main body 10, the clockwise and counterclockwise distances are (2L + x, 2L−x) and (4L−x, x).

  The left-right rotation distance difference (denoted as “difference” in Table 1) at each measurement point P1 to P6 in FIG. 4 is 0 and 4L (P1 and P6), 2x and 4L-2x (P2 and P5), 2L and 2L ( P3 and P4). Since the propagation delay time difference τ is proportional to the left-right turn distance difference and the sensitivity is proportional to the propagation delay time difference τ, the difference in Table 1 can be regarded as the sensitivity as it is. When the sensitivity of the optical fibers 14a and 14b with respect to the counterclockwise light and the clockwise light in the vibration detecting optical fiber 9 is added, it becomes 4L regardless of the place. This sensitivity characteristic coincides with the sensitivity characteristic of FIG.

  That is, in the optical fiber vibration sensor according to the present embodiment, even if vibration occurs in any part of the sensor cable 17, vibration can be detected with a certain sensitivity.

  In the embodiments so far, the length of the optical fiber 8b of the optical fiber delay unit 8 is 2L, the length of the vibration detection optical fiber 9 is 2L, and half of the length of the fiber loop unit 4 is the optical fiber delay unit. 8 corresponds to the optical fiber 8b.

  However, the present invention is not limited to this, and the same effect can be obtained if the length of the optical fiber 8b of the optical fiber delay section 8 is half or more of the length of the fiber loop section 4. When the length of the optical fiber 8b of the optical fiber delay unit 8 exceeds half of the length of the fiber loop unit 4, vibration detection at the main body connection points (for example, P1 and P6 in FIG. 4) in FIG. The signal intensity becomes greater than 0, the graphs of the sensitivity of the optical fibers 14a and 14b and the overall sensitivity are shifted upward, and the sensitivity (vibration detection signal intensity) becomes uniform regardless of the measurement point.

  FIG. 6B shows a return from the connection point of the sensor cable 17 with the vibration sensor main body 10 when the length of the optical fiber 8b of the optical fiber delay unit 8 exceeds half of the length of the fiber loop unit 4. FIG. 6 is a sensitivity characteristic diagram in which the distance to point C is taken on the horizontal axis and the vibration detection signal intensity based on the phase difference φ is taken on the vertical axis. As shown in FIG. 6 (b), the overall sensitivity is greatly improved.

  In the above-described embodiment, the entire length of the optical fiber 14 provided outside the casing 10a of the vibration sensor main body 10 is laid on a fence or the like as a measurement target as the vibration detection optical fiber 9. However, when detecting the vibration of the measurement object at a location away from the housing 10 a of the optical fiber vibration sensor 1, a part of the optical fiber 14 on the housing 10 a side needs to be used as the vibration detecting optical fiber 9. Absent. Accordingly, when the intermediate point M1 of the fiber loop portion 4 exists in the portion of the optical fiber 14 other than the vibration detection optical fiber 9, the length of the optical fiber 8b of the optical fiber delay portion 8 is the fiber loop portion 4. It may be less than half of the total length.

  In other words, when a part of the fiber loop part 4 constitutes the sensor cable 17 laid on the measurement object, if at least half of the fiber loop part 4 is outside the sensor cable 17, the optical fiber vibration sensor 1 vibration detection sensitivity can be improved. Further, by using the vibration detection optical fiber 9 composed of the optical fibers 14a and 14b arranged in parallel as the sensor cable 17, the vibration detection sensitivity of the optical fiber vibration sensor 1 can be made uniform.

  In the above embodiment, the phase modulator 6 is formed using the optical fiber 6b that is a part of the optical fiber constituting the fiber loop portion 4, and the phase of the propagation light is changed by applying a sine wave voltage of a predetermined frequency. Although the open-loop optical fiber vibration sensor to be modulated is configured, the present invention is not limited to this. You may comprise the closed loop type optical fiber vibration sensor which feeds back the phase of the propagation light detected to a phase modulator.

  In the above embodiment, the double coupler system using the first optical coupler 18a and the second optical coupler 18b is employed for the optical branching and coupling unit 5, but the present invention is not limited to this. An optical coupler having two ports at both ends may be used, a light source 2 and a light receiver 3 may be connected to one end, and the input / output side of the fiber loop unit 4 may be connected to the other end. Further, the polarizer 19 provided in the optical branching and coupling unit 5 may be omitted.

It is a block diagram of the optical fiber vibration sensor which shows one Embodiment of this invention. 2A is a perspective view of a polarizer, and FIG. 2B is a perspective view of a phase modulator. 3A is a perspective view of the optical fiber delay unit, and FIG. 3B is an explanatory view of the optical fiber delay unit viewed from the side. FIG. 2 is a substantial view of the optical fiber vibration sensor of FIG. It is a sensitivity characteristic figure of the fiber loop part in a Sagnac interference system vibration sensor. 6A and 6B are sensitivity characteristic diagrams of a sensor cable (vibration detecting optical fiber) according to the present invention. It is a block diagram of the conventional optical fiber vibration sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Optical fiber vibration sensor 2 Light source 3 Light receiver 4 Fiber loop part 5 Optical branch and coupling part 6 Phase modulator 7 Signal processing unit 8 Optical fiber delay part 9 Vibration detection optical fiber 17 Sensor cable

Claims (11)

A light source, a light receiver, a light branching and coupling unit for branching or coupling light, a signal processing unit for processing a received signal from the light receiver, and light branched by the light branching and coupling unit, respectively. A fiber loop unit that propagates as clockwise light; and a housing that houses the light source, the light receiver, the optical branch coupling unit, the signal processing unit, and a part of the fiber loop unit, and the optical branch coupling unit. In an optical fiber vibration sensor having one side connected to the light source and the light receiver and the other side connected to the fiber loop portion,
The optical branching and coupling unit includes: a first optical coupler to which the light source and the light receiver are connected; a polarizer that polarizes light from the first optical coupler; A second optical coupler that respectively enters the loop portion and couples the light emitted from the fiber loop portion,
The fiber loop portion is provided with a phase modulator,
A part of the optical fiber constituting the fiber loop portion is provided in the casing as a delay optical fiber, and the remaining optical fibers constituting the fiber loop portion are laid outside the casing as vibration detecting optical fibers. An optical fiber vibration sensor.   2. The optical fiber vibration sensor according to claim 1, wherein the delay optical fiber has a length at least half that of the optical fiber constituting the fiber loop portion.   2. The optical fiber vibration sensor according to claim 1, wherein the vibration detecting optical fiber is formed by connecting one end of two optical fibers arranged in parallel directly or using a folding optical fiber. .   2. The optical fiber according to claim 1, wherein the vibration detecting optical fiber has a folded portion of the fiber loop portion provided outside the housing, and is provided in a flexible tube. Vibration sensor.   The optical fiber vibration sensor according to claim 1, comprising: the housing; and the vibration detecting optical fiber provided detachably with respect to the housing.   2. The optical fiber vibration sensor according to claim 1, wherein the light source, the light receiver, the optical fiber used in the optical branching and coupling unit, and the optical fiber constituting the fiber loop unit are polarization plane preserving fibers. A light source;
A receiver,
A fiber loop with a loop structure that propagates counterclockwise and clockwise light;
One side is connected to the light source and the light receiver, and the other side is connected to the fiber loop unit. An optical branching and coupling unit that inputs to the receiver,
It consists of a phase modulator that gives a phase difference between counterclockwise light and clockwise light,
An optical fiber vibration sensor characterized in that a part of the fiber loop part constitutes a sensor cable laid on a measurement object, and at least half of the fiber loop part is provided outside the sensor cable.   The optical fiber vibration sensor according to claim 7, wherein the sensor cable includes two optical fiber portions arranged in parallel.   8. The optical fiber vibration sensor according to claim 7, wherein a part of the half of the fiber loop part constitutes an optical fiber delay part.   The optical fiber vibration sensor according to claim 7, wherein the optical branching and coupling unit includes a polarizer.   The optical fiber vibration sensor according to claim 7, wherein the two optical fiber portions are formed by folding one optical fiber.

Images